This invention relates to a magnetic disk for use in a magnetic recording device (HDD, Hard Disk Drive) or the like and a manufacturing method thereof. More specifically, this invention relates to a magnetic disk that can prevent a fly stiction trouble, a corrosion failure, and so on to suppress a malfunction and is thus excellent in safety even when a magnetic head performs a flying operation at a flying height of, for example, 10 nm or less, and a manufacturing method of the magnetic disk.
An LUL (Load Unload) system capable of higher recording capacity has started to be employed in HDDs (Hard Disk Drives) in recent years. In the LUL system, upon halting, a magnetic recording head is retreated to a slope bed called a ramp located outside a magnetic disk while, upon starting, the magnetic recording head is, after the magnetic disk starts rotation, slided from the ramp over the surface of the magnetic disk, and then recording/reproduction is carried out. Therefore, the magnetic recording head does not contact and slide on the magnetic disk.
In this LUL system, it is not necessary to provide a contact/slide region (CSS zone) for the magnetic recording head on the surface of the magnetic disk, which is required in the CSS system conventionally used. Therefore, it is possible to ensure a wider area of a recording/reproduction region as compared with the CSS system and thus increase the recording capacity of the magnetic recording medium. Further, in the LUL system, since the magnetic disk and the magnetic recording head do not contact each other, it is not required to provide texture for preventing contact adsorption, which is required in the CSS system, so that the surface of the magnetic disk can be made even smoother. Therefore, the recording density of the magnetic disk can be increased by reducing the flying height of the magnetic recording head as compared with the CSS system.
As such a magnetic disk, there is known a magnetic recording medium as disclosed in, for example, Japanese Unexamined Patent Application Publication (JP-A) No. 2003-248917.
On the other hand, in a magnetic recording device (HDD), volatile organic gases such as sulfur-based organic compound, chlorine-based organic compound, dioctyl phthalate, acrylic acid, and siloxane, acid gas, and so on are emitted at a certain ratio from various organic materials such as adhesives and plastic materials that are used in the device. Therefore, the organic gas, the acid gas, or the like tends to be adsorbed to a magnetic recording medium in an environment of, for example, high temperature and high humidity. Further, interaction occurs between the adsorbed gas and a lubricant of a lubrication layer so that the lubrication layer is liable to change in quality.
Such problems are becoming remarkable particularly following a reduction in flying height of a magnetic head. When the magnetic head flies over the surface of a magnetic disk at a low flying height (e.g. a small flying height of 10 nm or less), the magnetic head gathers up the organic compound etc. and the lubricant adsorbed on the surface of the magnetic disk, which tend to be transferred and deposited on the surface of the magnetic head. Particularly, in the case of a magnetic head having an NPAB slider (negative pressure slider), a strong negative pressure occurs at a lower surface (surface on the side of the magnetic disk) of the magnetic head to gather up, like a vacuum cleaner, the organic compound etc. and the lubricant adsorbed on the surface of the magnetic disk so that they tend to be transferred and deposited on the surface of the magnetic head.
If this transfer state exceeds a certain level, a trouble called a fly stiction phenomenon and a corrosion failure occur. The fly stiction is a trouble where the flying posture and height of the magnetic recording head go out of order during its flying operation and irregular changes in reproduction output occur frequently. According to circumstances, the magnetic recording head is brought into contact with the magnetic recording medium to crash during the flying operation, thereby destroying the magnetic disk. This fly stiction often occurs without a premonitory sign and is one of troubles that are difficult to control.
In the conventional CSS system, the CSS operation at the time of starting and stopping serves to perform cleaning of the lubricant and the organic compound etc. transferred to the magnetic recording head and, therefore, those troubles do not raise a problem.
On the other hand, in the LUL system, since there is no sliding movement between the magnetic recording medium and the magnetic recording head, there is no function of cleaning the lubricant and the organic compound etc. transferred to the head. Therefore, particularly in the LUL system, the lubricant and the organic compound etc. tend to be transferred and deposited on the magnetic recording head so that the fly stiction is liable to occur and a head element portion is liable to be corroded. Further, if this deposition advances, it often drops on the surface of the medium as deposits to damage a protection film to thereby enable recording and reproduction. Since the flying height of the magnetic recording head has still been reduced (10 nm or less) following the shift to the LUL system from the CSS system, the transfer and deposition onto the head has been further facilitated.
In addition, recently, magnetic disk devices such as HDDs (hard disk drives) have been often used in environments of low atmospheric pressures such as in an airplane. Following it, there has been arising a problem about flying stability of heads. Specifically, the flying height of the magnetic head further decreases from 10 nm due to a change in atmospheric pressure and, further, there occurs variation in flying height due to processing accuracy of air bearing sliders of the magnetic heads. As a result, a problem of the fly stiction has occurred frequently.
Further, recent magnetic disk devices such as HDDs (Hard Disk Drives) have been miniaturized and incorporated into digital cameras and music reproducing players. Under these circumstances, external pressures such as any environments (in airplane as described before, mountaintop, high temperature, low temperature, high humidity, low humidity) and any using manners (desktop, portable) affect flying properties (stable flying performance) of heads in magnetic disk devices and outgases from members in the magnetic disk devices.
As a cause for occurrence of the fly stiction, there can be considered the influence of roughness of the surface of the magnetic disk, interaction (meniscus force) between the lubrication layer and the head, or contamination due to outgas from the magnetic disk device.